linux-kernel - Re: [PATCH v10 01/15] modpost: fix removing numeric suffixes

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Date:   Tue, 3 May 2022 09:57:09 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Alexander Lobakin <alexandr.lobakin@...el.com>
Cc:     linux-hardening@...r.kernel.org, X86 ML <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        Ard Biesheuvel <ardb@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Bruce Schlobohm <bruce.schlobohm@...el.com>,
        Jessica Yu <jeyu@...nel.org>,
        kernel test robot <lkp@...el.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        Jonathan Corbet <corbet@....net>,
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        Nick Desaulniers <ndesaulniers@...gle.com>,
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        "H.J. Lu" <hjl.tools@...il.com>, Nicolas Pitre <nico@...xnic.net>,
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Subject: Re: [PATCH v10 01/15] modpost: fix removing numeric suffixes

On Thu, Feb 10, 2022 at 3:59 AM Alexander Lobakin
<alexandr.lobakin@...el.com> wrote:
>
> `-z unique-symbol` linker flag which is planned to use with FG-KASLR
> to simplify livepatching (hopefully globally later on) triggers the
> following:
>
> ERROR: modpost: "param_set_uint.0" [vmlinux] is a static EXPORT_SYMBOL
>
> The reason is that for now the condition from remove_dot():
>
> if (m && (s[n + m] == '.' || s[n + m] == 0))
>
> which was designed to test if it's a dot or a '\0' after the suffix
> is never satisfied.
> This is due to that `s[n + m]` always points to the last digit of a
> numeric suffix, not on the symbol next to it (from a custom debug
> print added to modpost):
>
> param_set_uint.0, s[n + m] is '0', s[n + m + 1] is '\0'
>
> So it's off-by-one and was like that since 2014.
> Fix this for the sake of upcoming features, but don't bother
> stable-backporting, as it's well hidden -- apart from that LD flag,
> can be triggered only by GCC LTO which never landed upstream.
>
> Fixes: fcd38ed0ff26 ("scripts: modpost: fix compilation warning")
> Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>
> ---


Acked-by: Masahiro Yamada <masahiroy@...nel.org>



>  scripts/mod/modpost.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 6bfa33217914..4648b7afe5cc 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1986,7 +1986,7 @@ static char *remove_dot(char *s)
>
>         if (n && s[n]) {
>                 size_t m = strspn(s + n + 1, "0123456789");
> -               if (m && (s[n + m] == '.' || s[n + m] == 0))
> +               if (m && (s[n + m + 1] == '.' || s[n + m + 1] == 0))
>                         s[n] = 0;
>
>                 /* strip trailing .lto */
> --
> 2.34.1
>


-- 
Best Regards
Masahiro Yamada